It has heretofore been proposed to provide a cased glass stream for forming glassware having layered wall segments. U.S. application Ser. Nos. 08/374,371 and 08/374.372, both now abandoned, disclose techniques for delivering such a cased glass stream in which core glass from a first source is delivered through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber that communicates with the second orifice through the gap between the first and second orifices. A heated tube delivers casing glass from a second glass source to the annular chamber that surrounds the second orifice. Glass flows by force of gravity from the first and second sources through the first and second orifices in such a way that a cased glass stream emerges from the second orifice. This cased glass stream may be sheared by conventional techniques to form individual cased glass gobs for delivery to conventional individual section glassware forming machines.
Although the techniques disclosed in the noted patent applications address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, a problem remains concerning uniformity of distribution of casing glass thickness around the circumference of the core glass stream. Above-referenced application Ser. No. 08/374,372, now abandoned, teaches that the dimensions of the metering gap between the first and second orifices, both in the direction parallel to glass flow therethrough and the direction perpendicular to glass flow therethrough, are chosen to provide uniform flow resistance to casing glass flow at all points circumferentially around each gap. In the preferred embodiments disclosed in that application, the dimensions of each gap, both parallel and perpendicular to glass flow, are uniform around the gap. In implementation of this technique, it has been found that the casing glass can vary in thickness by a ratio of up to 2/1 around the circumference of the core glass stream.
It is therefore a general object of the present invention to provide a method and apparatus for delivering a cased glass stream of the character disclosed in the above-noted applications that obtain improved uniformity of casing glass thickness around the circumference of the cased glass stream. Another and more specific object of the present invention is to provide a method and apparatus of the described character in which the metering gap between the aligned orifices is dimensioned with respect to the surrounding chamber and the feed from the source of casing glass so as to provide a more uniform resistance to casing glass flow throughout the entire casing glass flow path--i.e., from the casing glass feed around the chamber and through the metering gap. A further object of the present invention is to provide a method and apparatus of the described character in which a plurality of cased glass streams are formed by feeding core and casing glass through a plurality of orifice pairs surrounded by the casing glass chamber, and in which the metering gaps between all pairs of orifices are dimensioned with respect to each other and with respect to the surrounding chamber and the casing glass feed so as to provide substantially uniform and identical casing glass thickness at all of the cased glass streams.
Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass includes a first orifice for receiving core glass from a first source, and a second orifice vertically spaced beneath and aligned with the first orifice. A chamber surrounds the second orifice and communicates with the second orifice through a metering gap between the first and second orifices. Casing glass is delivered from a second source to one side of the chamber such that glass flows by gravity from both the first and second sources through the orifices to form the cased glass stream. In accordance with one aspect of the present invention, the metering gap between the orifices is of non-uniform dimension around the chamber, providing greater resistance to glass flow through the metering gap on a side thereof adjacent to the side of the chamber that receives casing glass from the second source and less resistance to glass flow through the metering gap on the side thereof remote from the side of the chamber that receives the casing glass.
In the preferred embodiments of the present invention, the metering gap between the orifices is dimensioned such that resistance to glass flow varies as a predetermined function of angle preferably a uniform function of angle, around the annular chamber and the metering gap. The dimension of the metering gap parallel to glass flow most preferably remains constant around the metering gap, while the dimension perpendicular to glass flow varies as a function of angle around the gap. Most preferably, the dimension of the metering gap perpendicular to glass flow varies by forming the opposed gap surfaces on angulated planes, so that this dimension varies trigonometrically around the gap.
In an implementation of the present invention having a plurality of first and second orifices disposed in aligned pairs and each separated by an associated metering gap, with all of the orifice pairs being surrounded by the casing glass chamber, at least one of the metering gaps is dimensioned differently from the other metering gaps to equalize resistance to glass flow as between or among the metering gaps from the source of casing glass through the chamber. In the preferred implementation of this aspect of the invention, three orifice pairs are disposed in a line parallel to the side of the chamber coupled to the source of casing glass. The metering gap at the center of the orifice pairs is dimensioned on a side thereof remote from the casing glass feed to provide less resistance to glass flow than at the corresponding sides of the other two orifice pairs. In this way, there is improved uniformity of resistance to glass flow from the casing glass feed through and around the chamber to both the front and back sides of the various metering gaps.